This application claims priority to Norvegian patent application Serial No. 1999.3251, filed Jun. 29, 1999.
Not applicable.
1. Field of the Invention
This invention relates to a surface loading buoy for transfer of petroleum cargo to an ordinary tanker vessel.
From the source or the upstream side the floating loading buoy receives the petroleum cargo from a petroleum production platform or ship via a flexible loading hose with an electrical (umbilical) cable. The floating loading buoy may possibly receive the petroleum cargo via a submerged loading buoy, e.g., a so-called STL-buoy from the upstream side. The invention comprises a surface loading buoy being arranged for connecting itself to ordinary tanker vessels, and to transfer the cargo directly to, ordinary tanker vessels. From these properties an abbreviation arises, which hereafter will be applied for a preferred embodiment of the invention, a DPDL-buoy: Dynamic Positioning Dock Loading buoy. The loading buoy, according to the preferred embodiment of the invention, is locked to the tanker vessel and takes over the dynamic position control over the vessel. The positioning control is conducted either by means of thrusters and dynamic positioning, or alternatively conducted by using the mooring system of a submerged turret loading buoy (STL-buoy) which normally is moored with a circular-spread anchor line system. Taking the control over the tanker vessel and conducting the position control can take place by a combination where the floating loading buoy, according to a preferred embodiment of the invention, picks up and hooks on to a tanker vessel and conducts a takeover of the physical control of it by means of the buoy""s thrusters, and thereafter it transfers the petroleum cargo from the STL-buoy via the DPDL-buoy to the tanker vessel. In an alternative preferred embodiment of the invention, the DPDL-buoy commands an STL-buoy to dock into an STL-dock in the bottom of the DPDL-buoy, and transfers the cargo.
2. Description of the Related Art
A side elevation view of parts of a tanker vessel 200 is shown in FIG. 3, and a simple cross-section of hull 210 and tanks are shown in FIG. 1. Ordinary tanker vessels 200 usually have a pipeline system for loading and offloading petroleum cargo with the vessel being loaded and unloaded via a midship manifold 230 directed out towards the hull""s side on the deck 220 of the tanker vessel. Such an arrangement is not normally directly applicable for offloading petroleum cargo from a floating loading buoy in the open sea, without making essential modifications. If the tanker vessel 200 becomes lying in a disadvantageous attitude with respect to the combined wind- and wave direction, it encounters strong side forces and it may show impossible to keep the vessel in position even though it may be provided with dynamic positioning systems (xe2x80x9cDPxe2x80x9d). Further, a floating loading buoy""s anchor lines normally are dimensioned to keep the buoy itself in a fixed position with respect to wind, waves and current, and may be also a tanker vessel if the tanker vessel is lying directed with the bow on the weather. The mooring lines are normally not dimensioned to keep a tanker vessel lying across the weather""s direction. Such loading buoys may comprise systems for transfer of cargo via fixed pipes or floating loading hoses running from the loading buoy to the bow 213 of the tanker vessel 200, with mooring lines between the loading buoy""s and the tanker vessel""s respective starboard and port sides.
Floating production, storage, and offloading vessels (FPSO-vessels) 300 are also known, with cargo transfer of petroleum happening via a floating loading hose arranged between starboard or port side of the FPSO""s stem, to the corresponding starboard or port midship manifold 230 with a manifold connector 337 on an ordinary tanker vessel 200. Damage and wear of such floating loading hoses are well known to people skilled in the art.
Submerged Turret Loading (STL)xe2x80x94buoys 331 are well known and are used for transferring cargo from a petroleum source 300 to a tanker vessel 200. The STL-buoy normally is arranged at the end of an STL-umbilical 332 which may comprise a loading hose or a riser pipe. The STL-buoy is adapted to be arranged at a distance below the sea surface to be raised as a plug for insertion into a corresponding STL-dock 233 arranged through the bottom 212xe2x80x2 of a specially adapted (modified) STL tanker vessel 200xe2x80x2, and with the STL-buoy at the same time being connected to a connector of a manifold coupled to pipelines leading to tanks on board the STL-tanker vessel 200xe2x80x2. STL-buoys usually are moored by means of at least eight anchor lines (340) arranged with anchors around the periphery. By means of the anchor lines 340 the STL-buoy 331 is kept in its position, and the vessel may normally lie freely pivotable in the STL-buoy 331. By means of ordinary STL-buoys a wire system on the tanker vessel is normally required for connecting to the STL-buoy, and communication devices for controlling the submergence and rise of the STL-buoy. Further it is required that the tanker vessel is specially designed with the particular STL-dock 333 having a shape of an inverted funnel-shaped vertical pipe channel arranged through the bottom of the vessel, ahead of midship of the tanker vessel 200xe2x80x2. The STL-dock is arranged for receiving and holding the STL-buoy, and is provided with connectors for the petroleum conductor in the STL-buoy, valves, valve control, and a pipe manifold arranged at the receiving part. The pipe manifold is connected to one or more pipelines leading to petroleum tanks in the tanker vessel. One problem in the known art is thus that such an STL-dock must be arranged in all dedicated vessels which are to receive an STL-buoy. This incurs huge costs in installing this equipment on tanker vessels 200xe2x80x2 during construction of new vessels 200xe2x80x2 or for refitting of ordinary tanker vessels 200.
The invention is constituted by a loading device for marine transfer of fluids via a flexible hose which preferably also has an electrical cable for power supply to the loading device, preferably petroleum fluid from an upstream source, e.g. a petroleum production platform, to an ordinary tanker vessel, and with a main hull comprising an underwater part and a part above the surface with a loading hose in a crane boom, arranged for transferring petroleum cargo from the flexible hose to the tanker vessel via the loading device. What is particular for the invention comprises the following features:
fixed contact surfaces constituted by the top surfaces of a longship pontoon and an athwartships pontoon respectively, arranged for being ballasted and deballasted for docking, by direct friction contact with the tanker vessel""s hull, preferably against the outer side of the tanker ship""s bottom, and
power devices arranged to move the loading device to and from a catching/holding position with the tanker vessel, and arranged for essentially controlling the position of the tanker vessel during the petroleum transfer operation.